In the manufacture of patterned devices such as semiconductor chips and chip carriers the steps of etching different layers which constitute the finished product are among the most critical and crucial steps involved. One method widely employed for etching is to overlay the surface to be etched with a suitable mask and then immersing the substrate and mask in a chemical solution which attacks the surface to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask such as by chemicals seeping under the mask and thereby continuing to attack the surface to be etched (isotropic etching), even under portions of the masked area. Such wet etching processes are also undesirable because of the environmental and safety concerns associated therewith.
Accordingly, various so-called "dry processes" have been suggested in the hope of improving the process from an environmental viewpoint, as well as reducing the relative cost of the etching. Moreover, the so-called "dry processes" have the potential advantage of greater process control, and higher aspect ratio images.
Such "dry processes" generally involve passing a gas through a container and creating a plasma in this gas. The species in this plasma are then used to etch a substrate placed in the chamber or container. Typical examples of such "dry processes" are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined vertically etched sidewalls. A particular reactive ion etching process is disclosed, for example, in U.S. Pat. No. 4,283,249 to Ephrath, disclosure of which is incorporated herein by reference.
One problem associated with "dry-processing" techniques is providing a patternable material which is sensitive to imaging radiation while, at the same time, being sufficiently resistant to the dry-etching environment. In many instances, resistance to the dry-etching such as to the plasma etching active species results in erosion of the mask material and loss of resolution of the material employed for preparing the mask in the lithographic exposure to the imaging radiation.
This is true for both positive organic resist materials and negative organic resist materials. A positive resist material is one which on exposure to imaging radiation is capable of being rendered soluble in a solvent in which the unexposed resist is not soluble. A negative resist material is one which is capable of polymerizing and/or insolubilizing upon exposure to imaging radiation.
One type of positive photosensitive material is based upon phenol-formaldehyde novolak polymers. A particular example of such is Shipley AZ1350 which is a m-cresol formaldehyde novolak polymer composition. Such is a positive resist composition and includes therein a diazoketone such as 2-diazo-1-naphthol-5-sulphonic acid ester. In such a composition, the diazoketone, during the photochemical reaction is converted to a carboxylic acid. This, in turn, converts a neutral-organic soluble molecule (the phenolic polymer) to one that is readily soluble in weakly alkali aqueous developer solvents. The composition usually contains about 15%, or so, by weight, of the diazoketone compound.
A discussion of various photoresist materials can be found, for instance, in the Journal of the Electrochemical Society, Vol. 125, No. 3, March 1980, Deckert, et al., "Microlithography-Key to Solid-State Fabrication", pp. 45C-56C, disclosure of which is incorporated herein by reference.
Additional discussion of the use of quinone diazides in light-sensitive applications can be found in "Quinone Diazides", Erschov, et al., Elsevier Scientific Publications, Amsterdam, 1981, Chapter 8, pp. 282-297, disclosure of which is incorporated herein by reference. In addition, it has been suggested therein to employ condensation products of 1,2-naphthoquinone-5-chlorosulphonic acid and certain silicon derivatives to improve the adhesion property of various films to a substrate whereby the condensation products are employed as light-sensitive backing therefor.
In addition, certain siloxanes have been suggested as reactive ion etch barriers. For instance, see Fried, et al., IBM, Journal Research Development, Vol. 26, No. 3, pp. 362-371. Also, certain siloxanes have been suggested as e-beam sensitive resists. For instance, see Roberts, Journal of Electrochemical Society, Vol. 120, p. 1716, 1973; Roberts, Phillips Technical Review, Vol. 35, pp. 41-52, 1975; and Gazard, et al., Applied Polymer Symposium, No. 23, pp. 106-107, 1974.
Moreover, there have been suggestions that certain siloxanes, when imaged with electron beam (see Hatzakis, et al., Processing Microcircuit Engineering (Lausanne), p. 396, September 1981); and deep U.V. at about 2537 Angstrom (see Shaw, et al., SPE Photopolymer Conference, November 1982) act as an etch mask for an underlying polymer layer in an oxygen plasma. However, these siloxane materials suggested require very limited methods for imaging (e.g.--e-beam and deep U.V.) and are not imageable with radiation of longer wavelengths (e.g.--greater than 2700A), where the majority of lithographic imaging tools, contact, proximity, and projection printers operate.